1. Field of the Invention
The invention relates to a method for identifying and correcting errors in time measurements on rotating shafts, particularly on crankshafts or shafts in internal combustion engines connected thereto.
Time measurement of this kind is effected in that the shaft itself or a tachometer disk connected thereto carry marks that are scanned by sensors. The time required by the shaft to traverse a specific angle of rotation is measured. In general, the rotational speed or rpm can be measured in this manner. More particularly, rpm fluctuations can be detected with arbitrarily accurate resolution at the circumference of the shaft or the tachometer disk, depending on the spacing of the marks.
Such measurements are used in internal combustion engines, for example, for identifying erratic combustion or misfiring via short-term slowing of the angular speed of the crankshaft. In the process the spacings of the markings on the crankshaft or the tachometer disk correspond to the stroke cycles of the individual cylinders.
However, if the markings or the tachometer disk have mechanical defects or inaccuracies, the angular speed measurement is distorted. For instance, angular errors of the segments or marking teeth of the tachometer disk, disk backlash or variance in the tooth formation can cause such distortions.